Dental materials

ABSTRACT

Dental materials containing monomers and/or prepolymers can be subjected to a polymer-forming reaction. The dental materials comprise at least one initiating system and optionally comprise fillers, colorants, flow modifiers, stabilizers, ion-releasing substances as well as compounds which increase X-ray capacity or other modifiers. The dental materials are characterized in that the initiating system is proportioned such that the dental materials are sufficiently capable of flowing for at least 10 seconds after exposure to oxygen, whereupon they subsequently harden into a solid material.

For some time the goal in dental medicine has been to replace theclassical filling material amalgam with composites (“plastics”). Incontrast to amalgam, it is necessary in the provision with composites touse a bonding agent. This so-called bonding is applied on the preparedhard tooth substance prior to the insertion of the composite into thecavity.

One important requirement of users of dental materials is that theprocessing be as simple as possible, that the processing not allow anyprocessing errors and that the desired results are always the same.

This requirement can be fulfilled at least to some degree when singlecomponent dental materials are prepared and processed.

The use of single component dental materials assumes that thepolymer-forming reaction can be initiated either by supplying energyand/or through reaction with components of “active” surfaces or thesurrounding atmosphere.

A typical case for the initiation of polymerization through the supplyof energy is photo-induced curing of dental materials, where irradiationwith light causes the decomposition of the photo initiators intopolymerization initiating species.

The curing rate of such photocuring dental materials is generally veryhigh, but curing takes place only in the areas reached by the light.

Due to the short lifespan of the polymerization initiating species, likethe free radicals, it is usually only possible to realize the exposureand thus the curing at the site of the end use of the cured dentalmaterial.

This circumstance restricts the use of photocuring for dental materials.Therefore, dental materials are desired that exhibit, as singlecomponent preparations, an adequate shelf life and that can be easily“activated”.

In this respect “activability” means that the polymerization initiatingspecies are produced in the dental materials taken from the storagecontainer through the introduction of energy and/or through reactionwith components having “active” surfaces or the surrounding atmosphere,provided that the dental materials can flow adequately freely for atleast another 10 seconds following “activation” in order to guarantee anapplication as intended.

Therefore, the object is to propose single component dental materialsthat exhibit stability in storage and an adequately long processingperiod after “activation”.

The problem of the invention is solved by dental materials, containingmonomers and/or prepolymers that are capable of a polymer-formingreaction; at least one initiating system, and optionally fillers, dyes,flow modifiers, stabilizers, ion-transferring substances, the x-rayopacity-increasing compounds or other modifiers, which are characterizedin that the initiating system is produced in such a manner that, whenbrought into contact with oxygen, it releases species initiating thepolymer-forming reaction; and the quantity of initiating system isdimensioned in such a manner that after bringing into contact withoxygen the dental materials can flow adequately freely and can beprocessed for at least another 10 seconds and thereafter cure to asolid.

The resulting smear layer is preferably less than 0.2 mg/cm².

According to the invention, an oxygen sensitive compound is used, thatwhen brought into contact with oxygen, can form an excited or reactivespecies, preferably radicals that in turn can release acid from a salineinitiator by means of another reaction sequence. Said acid can initiatea polymerization reaction, in particular a cationic polymerizationreaction.

This saline initiator is, for example, iodonium compounds, which, whenactivated, for example, by means of free radicals, can decompose intoacids.

Thus, there are two initiator systems, which react with each other, tocontrol the course of the polymerization reaction.

According to a preferred embodiment of the invention, the dentalmaterials are taken from the sealed, oxygen-impermeable storagecontainer and brought into contact with the ambient air within a periodranging from 1 to 120 seconds. At the same time it is expedient toprovide new surfaces by filling and slightly mixing, a feature thataccelerates the “activation”.

According to another embodiment of the invention, the dental materialsare applied on “active” surfaces that release oxygen, whereby the oxygencan be produced, for example, through reaction of a compound, located onthe surface, with a component of the liquid dental materials.

The dental materials, according to the invention, cure so as to form apolymer, whereby preferably such monomers or prepolymers are used thatpolymerize according to a cation chain mechanism, by means of athiol-ene mechanism or according to a radical chain mechanism.

Combinations of several mechanisms are also possible.

Thus, the dental materials can contain monomers and prepolymers thatcure by means of ring-opening polymerization, whereby the use ofcompounds containing at least two epoxide groups is preferred.Cycloaliphatic epoxide resins, which cure according to a cationic ringopening mechanism, constitute a class of monomers that can be usedadvantageously.

Typical representatives of these cycloaliphatic epoxide resins aredescribed, for example, in the DE-A-196 48 283 A1.

The dental preparations, which cure according to a thiol-ene mechanism,contain multi-thiol compounds, like the tetramercaptopropionate ofpentaerythritol, and multi-allyl compounds, like triallyl isocyanurate.

Such dental materials, based on thiol-ene systems, are described indetail in the DE-A 3837569, to which reference is made here.

Typical monomers or prepolymers that cure according to a radical chainmechanism and are used in dental materials are acrylates ormethacrylates. Suitable are generally uni- or multi-functional(meth)acrylate monomers. Typical representatives of this class ofcompounds are alkyl(meth)acrylates, including cycloalkyl(meth)acrylates,aralkyl(meth)acrylates and 2-hydroxyalkyl(meth) acrylates, likehydroxypropyl methacrylate, hydroxyethylmethacrylate, isobornylacrylate, isobornyl methacrylate, butyl glycol methacrylate, acetylglycol methacrylate, triethylene glycol dimethacrylate, polyethyleneglycol dimethacrylate, 2-phenylethylmethacrylate, 2-ethylhexylmethacrylate, cyclohexyl methacrylate, lauryl methacrylate andhexanedioldi(meth)acrylate, as described in the DE-A 4328960.

Long chained monomers, based on bisphenol A and glycidyl methacrylate ortheir derivatives, produced through the addition of isocyanates, asdescribed in the U.S. Pat. No. 3,066,112, can also be used. Suitable arealso the compounds of the type bisphenyl-A-diethyloxy(meth)acrylate andbisphenol-A-dipropyloxy(meth)acrylate.

Furthermore, the oligoethoxylated and oligopropoxylatedbisphenol-A-diacrylic and dimethacrylic acid esters can be used. Quitesuitable are also the diacrylic and dimethacrylic acid esters, which arementioned in the DE-C 2816823 and belong tobis(hydroxymethyl)-tricyclo[5.2.1.0^(2,6)]-decane, and the diacrylic anddimethacrylic acid esters of the compounds ofbis(hydroxymethyl)-tricyclo [5.2.1.0^(2,6)]-decane, which are extendedwith 1 to 3 ethylene oxide and/or propylene oxide units. This list isintended as an example and not to be understood as conclusive by anymeans.

Mixtures of the aforementioned monomers can also be used.

The inventive dental materials contain at least one initiating system,which upon contact with oxygen releases the species initiating thepolymer-forming reaction.

Preferably the dental materials contain compounds, which are rapidlyoxidized by means of oxygen, whereby free radicals are formed by thisreaction or by successive reactions. Said free radicals initiate eitherdirectly the polymer formation or form, after reaction with othercomponents of the liquid dental preparations, the species initiating thepolymer-forming reactions.

Suitable classes of compounds subject to rapid oxidation by means ofoxygen are, for example, substituted hydrazones and boranes.

Thus, the autoxidation of hydrazones is already described in the Report47 (1994) pp. 3277 to 3291.

Hydrazones-containing multicomponent mixtures, which are capable ofundergoing free radical polymerization by means of the addition ofatmospheric oxygen, are described in the DE-A 4000776, column 2 (line67) to column 9 (line 41), to which explicit reference is made withrespect to the disclosure.

Preferably the hydrazone compounds, described in the EP-A 0510035 and inthe EP-A 0594671, can also be used. These hydrazones are capable offorming hydroperoxides and are usually used as polymerization startersfor monomers that are capable of undergoing free radical polymerization.

In a preferred embodiment of the present invention hydrazones of thedescribed type are used together with iodonium compounds, in particularbisaryliodonium salts of stronger acids, to cure preparations containingepoxide group-containing monomers.

The DE-A 3041904 describes boron compounds-containing plastic compoundsthat cure after making contact with oxygen and that are used especiallyas reaction adhesives.

In the DE-A 3201780 new polymeric organoboron compounds are proposedthat impart to the multicomponent mixtures, which are capable ofundergoing free radical polymerization, an improved stability duringhigh initiating action.

The EP-A 0835646 describes adhesive compositions, which contain organicboron compounds and can be used, among other things, in dentalmaterials, like bondings.

A common feature of the aforementioned proposed solutions is that theyrelate exclusively to free radical curing preparations and that theimportant demand of users of dental materials for a preparation that isas simple as possible and for constancy of preparation results isfulfilled to a very limited degree.

The inventive preparations and processing techniques expand the possiblepolymer-forming reactions by the cationic ring opening polymerizationand thiolene systems, thus achieving adequate shelf life and simpleprocessibility.

In preparations, which are capable of free radical polymerization,properties extending far beyond those described in the state of the artare obtained.

With the use of monomers or prepolymers, which cure by means of acationic ring opening polymerization, not only compounds reacting withoxygen, like hydrazones or boranes, but also the presence of compoundsthat decompose under the influence of radicals so as to form acids arenecessary.

For this embodiment of the invention, acid formers, as described indetail in the DE-A 19736471, have proved to be especially appropriate.

Based on the total preparation, the inventive dental materials usuallycontain 0.1 to 10% by weight, preferably 0.2 to 5% by weight andespecially preferred 0.5 to 3% by weight of initiator, and based on thetotal preparation, usually 90 to 99.9% by weight, preferably 95 to 99.8%by weight and especially preferred 97 to 99.5% by weight of monomers orprepolymers or their mixtures.

When this combination of compounds is used, it is also possible to curemonomer mixtures that contain substances, which are capable ofundergoing only free radical or only cationic polymerization, and thatcontain both classes of substances.

The dental materials, according to the invention, may or may not containfillers, dyes, flow modifiers, stabilizers, ion-transferring substances,the x-ray opacity increasing compounds, or other modifiers.

Suitable fillers are, for example, substances, described in the DE-A19648283 (page 10, lines 48-59).

When the inventive dental materials contain fillers, they comprise:

a) preferably 0.1 to 10% by weight, in a more preferred manner 0.2 to 5%by weight and in an especially preferred manner 0.5 to 3% by weightinitiator,

b) preferably 3 to 84.9% by weight, in a more preferred manner 5 to 75%by weight and in an especially preferred manner 20 to 75% by weightfillers,

c) preferably 15 to 96.9% by weight, in a more preferred manner 20 to94.8% by weight and in an especially preferred manner 22 to 79.5% byweight monomers or prepolymers or their mixtures.

If in addition the compositions contain one or more of theaforementioned additional additives, like dyes, flow modifiers etc.,they are present in quantities that are customary in the dental sector.

One special advantage of the inventive preparations and processingtechniques lies in the fact that the range of the “activation time” andthe “processing time” is determined by the composition of the activabledental materials; and the processor can influence within specific limitsthe requisite “processing time” by means of the intensity with whichsaid materials are brought into contact with oxygen or air.

The dental materials, according to the invention, are packed intosuitable containers, which are preferably oxygen and light impermeable,for use according to the instructions. Suitable containers arecartridges, mixing capsules, compules, or tubes.

EXAMPLES Embodiment 1

In a triple arm kneader the substances, described below, are kneadedinto a homogeneous paste under nitrogen in a dark room.

The paste is evacuated; the vacuum is filled with nitrogen and the pasteis put into light and oxygen impermeable dosing containers.

Gram based on Composition of the paste: 100 g of pastebis(4-dodecylphenyl)iodoniumtetracis(pentafluoro- 0.62 phenyl)borate3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcar- 14.19 boxylate1,3,5,7-tetracis-(2,1-ethanediyl-3,4-epoxycyclohexyl)- 7.811,3,5,7-tetramethylcyclotetrasiloxane quartz, average particle size 2micrometers, silanized 66.51 with epoxysilane tributylborane* 0.472-butoxyethyl-4-dimethylaminobenzoate 0.08 dilithiumcarboxylate of apolyethylene glycol 600 diacid 0.11 bisphenol-A-monoglycidethermonomethacrylate 10.21 (UVACURE 1561) *Polymeric boron alkyl B2,prepared according to the data in Table B of the DE-A 3201780.

The paste was used to cement crowns.

To this end, 0.3 g of the paste was removed from the dosing containerand put on a silicone paper block, slightly kneaded with the spatula for20 seconds, filled into the crown and the filled crown is mounted on theprepared stump.

The projecting paste could be easily removed after 2 minutes.

The cemented crown was functional ten minutes after mounting on thestump.

In light and oxygen impermeable dosing containers the product is stablein storage for 18 months.

Another application of the inventive preparations is in the area oftemporary crowns and bridges. The dentist prepares them usually in sucha manner that before the preparation he takes an impression of themomentary tooth situation, for example, with a silicone precisionimpression material.

Following preparation of the tooth or the teeth, they need temporaryprotection and are provided with a temporary crown or bridge. To thisend, the situation impression is filled with an appropriate material,the mixed temporary crown and bridge material. Then the filledimpression is put on the prepared tooth stump and cured up to theelastic phase in the mouth. During the elastic phase the material isremoved and allowed to stand at room temperature until it is completelycured. After curing, the material usually exhibits a so-called “smearlayer”. It is usually created by means of oxygen on the surface inconnection with the inhibition of radical polymerization.

Before the dentist can continue to process the temporary structure, thesmear layer has to be removed, a step that means a considerable amountof work. The use of the preparations, according to the invention, hasdemonstrated that virtually no smear layer is created and thus thissignificant drawback has been eliminated. The preparations, listedbelow, are embodiments and do not by any means constitute restrictions.

Embodiment 2

Two component material for temporary crowns and bridges, which is mixedin a ratio of 10/1 (base/catalyst) and cured without any smear layer.

The base paste and the catalyst paste are admixed from the components,listed in Table 1, under nitrogen by means of kneading.

Gram, based on 100 g of paste: Base paste: pyrogenic silicic acid 5.00(particle size < 0.05 micrometers) glass powder, silanized 32.50(average particle size 10 micrometers) 2,2-bis(4-(oligo(ethoxy))- 61.48phenyl)propanedimethacrylate N,N-dimethyl-p-toluidine 0.50 hydroquinonemonomethyl ether 0.02 tributylborane* 0.50 Catalyst paste: glass powder,silanized 32.00 (average particle size 10 micrometers)2,2-bis(4-(oligo(ethoxy))-phenyl)- 65.50 propane diacetatebenzoylperoxide (peroxide chemistry) 2.50 *Polymeric boron alkyl B2,prepared according to the data in Table B of the DEA 3201780.

The use of the temporary crown and bridge preparation, according toembodiment 2, results in a “total smear layer”, for which a numericalvalue of <0.2 mg/cm² was found in accordance with the detection limit ofthe method described below.

Comparison Example 1

With the use of a silicone impression material, a commercial, freeradical curing temporary material shows a smear layer (for determinationsee below) on both the temporary material (approx. 1.6 mg/cm²) and theimpression material (approx. 1.2 mg/cm²). The “total smear layer” yieldsa numerical value of approximately 2.8 mg/cm².

Method for Determining the Smear Layer

The smear layer is determined as follows:

A Delrin ring (DuPont) (d=20 mm; h=3.5 mm) is placed on a platelet madeof the impression material (AP), filled with the sample material (PM)without bubbles, covered with a microscope slide, and cured at roomtemperature for one hour. After the slide is removed, the test specimenis pushed out, and the sample material and the impression material withthe smear layer are weighed (yields m1 and m2).

Then the smear layer is removed from the AP and PM with paper moistenedwith ethanol. The weighing yields the mass of AP and PP without smearlayer (m3 and m4). The total smear layer is derived from:$S = \frac{{m(a)} - {{m(b)}\lbrack{mg}\rbrack}}{F\lbrack {cm}^{2} \rbrack}$

m(a) : m1+m2 (total mass (AP+PP) with smear layer)

m(b): m3+m4 (total mass (AP+PP) without smear layer)

area F=d²[cm]*π/4=3.142 cm²

Embodiment 3

Two component material for temporary crowns and bridges, which is mixedin a ratio of 10/1 (base/catalyst) and cured without any smear layer.

The preparation is produced as described under embodiment 2.

Gram, based on 100 g of paste: Base paste: pyrogenic silicic acid 5.00(particle size < 0.05 micrometers) glass powder, silanized 32.50(average particle size 10 micrometers) 2,2-bis(4-(oligo(ethoxy))- 49.00phenyl)propanedimethacrylate bisphenol-A-monoglycidether 12.00monomethacrylate (UVACURE 1561, company: UCB) tributylborane* 1.00diphenyliodonium- 0.50 hexafluorophosphate (company: Avocado) Catalystpaste: glass powder, silanized 32.00 (average particle size 10micrometers) 2,2-bis(4-(oligo(ethoxy))-phenyl)- 65.00 propane-diacetatebenzoylperoxide (peroxide chemistry) 2.50 *Polymeric boron alkyl B2,prepared according to the data in Table B of the DE-A 3201780.

The use of the preparation, according to embodiment 3, results in a“total smear layer”, for which a numerical value of <0.2 mg/cm² wasfound.

What is claimed is:
 1. A dental material which cures to a solid througha cation chain mechanism, comprising: at least one ingredient selectedfrom the group consisting of epoxide group containing monomers andepoxide group containing prepolymers; a first initiating system; and asecond initiating system, wherein said first initiating system iscomprised of at least one compound selected from the group consisting ofboranes and hydrazones and releases species initiating a polymer formingreaction upon contact with oxygen, wherein said second initiating systemis comprised of iodonium compounds capable of radical fission, andwherein said first initiating system and said second initiating systemare present in an amount allowing for at least 10 seconds of oxygencontact before the dental material becomes a solid.
 2. Dental materials,as claimed in claim 1, wherein the dental materials cure after contactwith air.
 3. Dental materials, as claimed in claim 1, wherein the dentalmaterials contain double bond-containing monomers.
 4. Dental materials,as claimed in claim 1, wherein the dental materials cure by means of acationic ring opening polymerization.
 5. Dental materials, as claimed inclaim 1, wherein the dental materials contain epoxide group-containingmonomers and at least one ingredient selected from the group consistingof double bond-containing monomers and double-bond containingprepolymers.
 6. Dental materials, as claimed in claim 1, wherein thedental materials contain acryl group-containing monomers and prepolymersand cure by means of a radical chain mechanism.
 7. Dental materials, asclaimed in claim 1, wherein the dental materials contain allylgroup-containing monomers and norbornene group-containing monomers andmulti-thiol compounds and cure according to a thiolene mechanism. 8.Dental materials, as claimed in claim 1, wherein the dental materialscontain diaryl iodonium compounds.
 9. Process for curing dentalmaterials, as claimed in claim 1, wherein prior to their application thedental materials are stored in light and oxygen proof containers, andwherein the dental material is removed from said container and broughtinto contact with the ambient air for a period ranging from 1 to 120seconds.
 10. Process for curing dental materials, as claimed in claim 1,wherein oxygen is produced in the dental materials by means of achemical reaction with an oxygen releasing surface.
 11. Process forcuring dental materials, as claimed in claim 1, wherein prior toapplying the dental material an oxygen releasing surface is produced bydoping a surface with an oxygen rich material.
 12. Process for curingdental materials, as claimed in claim 1, comprising: removing paste formdental materials from a container; applying the dental materials to asubstrate using a hand tool within a range of 1 to 60 seconds; andexposing the dental materials to air, wherein upon exposure to air thedental materials cure to a new surface.
 13. Process for curing dentalmaterials, as claimed in claim 1, wherein the dental materials aretreated with an air current following application.
 14. Application ofdental materials, as claimed in claim 1, for a use selected from thegroup consisting of: fastening crowns, fastening bridges, fasteninginlays, filling cavities, treating mechanically prepared cavities, andtreating cavities pretreated by means of an etching step.
 15. A dentalmaterial which cures to a solid through a cation chain mechanism,comprising: at least one ingredient selected from the group consistingof epoxide group containing monomers and epoxide group containingprepolymers; a first initiating system; and a second initiating system,wherein said first initiating system is comprised of at least onecompound selected from the group consisting of boranes and hydrazonesand releases species initiating a polymer forming reaction upon contactwith oxygen, wherein said second initiating system is comprised ofiodonium compounds capable of radical fission, wherein said firstinitiating system and said second initiating system are present in anamount that allows the dental material to cure to a solid after contactwith oxygen, and wherein the unpolymerized monomer layer on the surfaceis less than 0.2 mg/cm².
 16. Dental materials, as claimed in claim 15,wherein the ratio of said first initiating system and said secondinitiating system is such that following contact with oxygen the dentalmaterials can flow freely for at least 10 seconds and thereafter cure toa solid.
 17. A kit, comprising: a container holding dental material, asclaimed in claim
 15. 18. A method of producing temporary crowns andbridges, comprising applying dental material according to claim 15 to asurface.
 19. A curing material for polymer-forming preparations,comprising: a first initiating system comprising an oxygen sensitivesubstance selected from the group consisting of boranes and hydrazones;and a second initiating system comprising at least one iodonium compoundwhich decomposes under the influence of radicals and forms acids.
 20. Acuring material for polymer-forming preparations, as claimed in claim19, wherein said second initiating system is a diaryl iodonium compound.21. A curing material for polymer-forming preparations, as claimed inclaim 19, wherein the polymer-forming preparation comprisesepoxide-containing substances.
 22. A method to set the processing timeof a dental material, comprising application of a curing material forpolymer-forming preparations according to claim
 19. 23. The dentalmaterial of claim 1, further comprising at least one ingredient selectedfrom the group consisting of fillers, dyes, flow modifiers, stabilizers,ion-transferring substances, x-ray opacity increasing compounds, andfurther modifiers.
 24. The dental material of claim 15, furthercomprising at least one ingredient selected from the group consisting offillers, dyes, flow modifiers, stabilizers, ion-transferring substances,x-ray opacity increasing compounds, and further modifiers.
 25. A kit,comprising a container holding dental material according to claim 1.